No registration or passwords; no pop-up ads -- just aloha, fun, & answers.
(as an eBay Partner & Amazon Affiliate earns from qualifying purchases).
Home /
T.O.C.
Fun
FAQs
Good
Books
Ref.
Libr.
Advertise
 
Help
Wanted
Current
Q&A's
Site 🔍
Search
pub  Where the
world gathers for metal finishing
Q&As since 1989



-----

Black stains on aluminum from shipping




I work for a metal shop as QA Engineer. We fabricate aluminum enclosures for electronic devices which are plated by a subcontracted supplier. Plating is clear chromate according MIL-5541 type II class 3.

Weeks ago we detected some black stains over the parts which matched the pattern of creases in the polyurethane bag used for package parts. When removing the stain we found out that the aluminum under it had been "degraded"

We verified cleanliness of bags used, dry times on plating but we found nothing wrong.

Today we just received a complaint from our customer in regards of same issue. We are for sure that we did not ship stained parts so the marks or stains must appear after we ship the parts.

Our supplier is clueless as what could be causing such condition. Help is highly appreciated.
Regards

Isela Rodriguez
sheet metal employee - Chihuahua Mexico
April 21, 2009



Class 3 at best is not much corrosion protection and is obviously adsorbing fumes from the poly packaging that degrades the thin (to nothing) coating. Recommendation: (1)package in certified sulfur free white paper, and/or (2) use Class 1A full yellow thick and heavy chromate.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
April 23, 2009



May 19, 2009

Estimado Ingeniero

Haz trtado bolsas de silica gel? por otra parte lo que te mencionan anteriormente puede coincidir ya que yo tuve el mismo problema con mi cliente sobre cold roll pero el hecho de que empaques piezas:
Calientes,
Humedas,
Mal Tratamiento de Cromo
Bajo pH
Alto pH
Indica una mala aderencia del cromato con lo cual aparecen manchas blancas you obscuras.

Saludos

Sergio Samaniego
Mexicali, Baja California, Mexico


----
Ed. note: Sincere apologies, Sergio, but this conversation can't continue in Spanish. This is a monitored site where we attempt to limit commerciality, flaming, etc., and I am unable to do that in languages other than English. Also, we solicit help from a long list of "regular readers" who also don't speak Spanish. Sorry, but postings must be in English. Regards, -- Ted.



(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact  -  Privacy Policy  -  ©1995-2024 finishing.com, Pine Beach, New Jersey, USA  -  about "affil links"